The effect of sex and the supplementation of the prebiotic, mannan oligosaccharides (MOS), the acidifier, calcium propionate (CPr) or their combination in the feed of Japanese quail (Coturnix japonica) on their performance and carcass quality was examined in this experimentation. Three hundred, 1-day old Japanese quail were divided into four groups with three replicates each. One group that served as control received the basal diet. The three experimental diets consisted of the basal diet to which either 6 g CPr/kg, 2 g MOS/kg or both 2 g MOS/kg and 6 g CPr/kg was added. The body weight, feed consumption, feed conversion ratio (kg feed/kg weight gain) and mortality were examined at weekly intervals. At the end of the 42-day feeding period the birds were slaughtered, the carcasses were processed and the carcass weight, carcass dressing percentage and carcass part percentages were calculated. Also, the breast meat composition and its fatty acid profile were analyzed. Results showed that the female quail had a higher body and carcass weight and liver to live weight percentage, whereas they had lower carcass dressing percentage than males. The dietary addition of MOS increased body and carcass weight, whereas it decreased liver to live weight percentage and crude fat content of the breast meat. The dietary addition of CPr lowered carcass dressing percentage and ash content of the breast meat. Interactions between the two examined supplements were observed in feed consumption, feed conversion ratio and carcass weight. An interaction between MOS and sex was observed on carcass weight. It was concluded that MOS and calcium propionate can be used effectively in Japanese quail diets.